Our overall goal is to build a micro-invasive blood volume monitor (BVM) to provide information to the physician on how best to treat hypotension that is prevalent in patients with burn or trauma, and patients undergoing hemodialysis. The basic rationale is to measure the change in ultrasound velocity of blood following isotonic saline infusion for the determination of the change in gravimetric density of blood and then the blood volume. In Phase I, we constructed ultrasound density probes (UDP) in three designs. The feasibility of two of the three to assess blood volume was demonstrated with in vivo dog experiments. Built on the experience we gained in Phase I, the specific aims of this Phase II research and development are: 1.To improve the resolution (by a factor of 2 to 3) and clinical viability of UDP with better signal processing package, designs more suitable for clinical use, and new intravascular versions. 2.To empirically verify the universal (or one-to-one) relation between the density and ultrasound velocity over the range that can occur in patients with trauma or burn. 3.To use the dog as a model to examine a spectrum of clinical conditions in which the proposed methodology can provide accurate assessment of blood volume. The BVM built through this process will allow us to proceed into Phase III for a full clinical trial aiming to examine whether blood volume assessment can detect early cardiovascular deficiency and project a course of therapy for the prevention of hypotension and/or low cardiac output. PROPOSED COMMERCIAL APPLICATIONS: This SBIR grant is to develop a micro-invasive blood volume monitor (BVM) (1) to assist the physician in designing an effective fluid replenishment strategy for patients with burns or trauma, (2) to improve current hemodialysis aiming to prevent the development of hypotension, and (3) to yield a better index than the arterial pressure in assessing the patient's cardiovascular function.